This invention relates generally to printers and more specifically to high-speed thermal printers.
Traditionally, thermal printers contain a thermal print head that having one thermal element for each dot that can be imaged on the paper. For example, a typical traditional thermal print head, that has a printing granularity of 8 dots per millimeter, will have eight thermal elements per millimeter. A four-inch wide printer will have over eight hundred thermal elements to form a complete four-inch row of print.
Each thermal element can be individually controlled in such a manner to allow the thermal element to be on or off to form the dot pattern necessary in creating a dot of the image to be printed. The thermal elements have a resistive component and are heated by applying a voltage of sufficient amplitude and time duration to raise the temperature of the thermal element to a point that causes the thermally active paper to change color and form a dot. Typically, 0.3 mill-joules of power are required to image a dot.
A limiting factor for the printing speed of this technology is the fact that the thermal elements retain heat. The heat is normally transferred to a heat sink that is part of the print head mechanism. The printer industry terms the capacity of a thermal print head to store heat the heat storage coefficient. Stated alternately, this is the rate at which the print head removes the heat generated by the thermal printing process. If the head temperature rises to a predefined temperature, the printing process must. slow down or stop to prevent damage to the thermal elements on the thermal print head.
Practical field experience with traditional thermal print heads that there are areas in need of improvement in the current thermal printer designs and implementation related to improved methods and means of printing images on a variety of thermally active media. Specifically, use thermal print heads having resistive elements and incorporating heat sinks